Composition control of aqueous ammonia solution by differential pressure



March 4, 1958 D. E. BERGER 2825,53@

COMPOSITION CONTROL OF' AQUEOUS AMMONIA V SOLUTION BY DIFFERENTIAL PRESSURE Filed April 30, 1954 3 Sheets-Sheet 2 H11-"CYCLE H20 rr :X2 I

S s s f e 1 Q f Q i Flea/H NH3 FLASH THA/K .5/

D/FFf/efA/r/AL PRESSURE 49 ammo/ LER FHaM HHH NH3 5mn/16E 400A' NH3 T0 PRCESS INVENTOR BY BEveIfgeI/f www A TTOE'NE K5 March 4, 1958 D. E. BERGER 2,825,630

COMPOSITION CONTROL OF AQUEOUS AMMONIA SOLUTION BY DIFFERENTIAL PRESSURE Filed April 30, 1954 5 Sheets-Sheet 3 I y@ M ,f 7a N @SQSQ 50 QSQ l 40 20 //1/ /0 W15/@HT PER CENT AMMONIA /lV WATER a* www? PRESSURE (PS/4) 4o 50 60 70 60 90 100 11a /20 fsa 14o 15a fda 170 fao /a 200 220 o TEMPERATURE "F INVENTOR.

TTORNEYS United States Patent O CONIPOSITION CONTROL F AQUEOUS AM- MONIA SOLUTION BY DIFFERENTIAL PRES- SURE Donald E. Berger, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application April 30, 1954, Serial No. 426,787 8 Claims. (Cl. 23-193) This invention relates-to a process for making substituted pyridinesl by the condensation of analdehyde or a ketone with ammonia. In one of its aspects this invention relates toa means for controlling aqueous ammonia concentration fed to a substituted pyridine reactor. In a more specic aspect, this invention relatesito an improved methodforcontrolling the ammonia concentration in an aqua ammonia stream produced-by an ammonia absorber.

The condensation ofraldehydesv and ketones, either saturated or unsaturated, and derivatives thereof withV ammonia'or its derivative to form substituted pyridines is oneof the oldest of organic reactions. See R. L. Frank etrval., Journal of the American Chemical Society 71, pages 2629 et-seq. (August 1949), and R. L. Frank-et al., JournalA of*V the American Chemical Society 68, pages 136sf9 (July 1946).

a One methodfor producing these substituted pyridine products is to reactan aqueous solution of ammonia with an aldehyde, ketone or derivative thereof at elevatedtemperature and Vgenerallyin the presence of a catalyst. I will. refer to the aldehydes, ketones and derivatives thereof as carbonyl compounds throughout this discussion. This synthesis step requires an aqueous ammonia stream of.

25 to 40 .Weight percent ammonia. When the ammonia concentration is too. high, theV excess ammonia leads to overloading of the recovery equipment. Too low` ammonia coneentrationleads to low conversion or reaction elii'ciency because the carbonyl will be incompletely convertedl or will be partially consumed by side reactionsin the .absence of Ysometexcessammonia.y As has been said, the synthesis can utilize Vammonia solutionv in the con.

mo'nia concentration and to control the selected concenv tration `within'plus or minus 2 percent.V With this strict control onlyminor surges in the process are encountered which'are readily tolerated. .Ammonia for this process ispreparedby dissolving ammonia in water in an kabslorbferl), Three sources contribute ammonia to the ab sorber, namely fresh anhydrous ammonia, recycle ammonia flashed froml the reactor,.and ammonia stripped from the product as will be seen from the detailed discussion. of this invention. The last two named sources of ammonia are subject to variations in the process and therefo'rea pre-setow of anhydrous ammonia will lead tp` comparable variations in the ammonia concentration prepared inthe absorber. While my invention is pri marily concerned with controlling the ammonia concentration in aqueous solution for feeding a synthesis unit for producing pyridine derivatives by condensationeof a carbonyl compound with ammonia, it will be obvious to those skilledin the art that the absorber and method of this invention can `be used wherever aqueous ammonia is being prepared. When such a solution is prepared by simplyadding anhydrous ammonia to water, such contrgl not especially required. This invention is parfr ice ticularly useful'where aqueous ammonia is being pre1-v Apared from a source of anhydrous ammonia in conjunc-` tion with one or more streams of ammonia of variable iiow. Y

An object of this invention is to provide a method of controlling the concentration of ammonia inaqueous solution prepared in ,an ammonia absorber.y Another obv ject of this invention is to provide an apparatus for pref. paring aqueous ammonia of a predetermined concentration. Still another object of this invention is to provide a method andapparatus for controlling the aqueous ammonia concentration in the synthesis of pyridinev deriv.

Aatives by condensing a carbonyl compound with ammonia.

- Y'Ashes been said, this invention is particularly useful in the preparation of pyridine derivatives by 'the con?, densation of a carbonyl compound with ammoma and Afor that reason, I will further explain this invention in terms of such av reaction. As has been said, the condensation of a carbonyl compound with ammonia 'to' form pyridine derivatives-'is one of the oldest in the art and no lengthy discussion is needed here. The carbonyl compounds are known in the art and illustrative ,examples are set forth in detail in the above-named Frank et al. references.; Some examples are acetaldehyde, crotonaldehyde, crotonaldehyde diethyl acetal, paraldehyde, benzalacetophenone, benzaldiacetophenone, ethylideneacetone, para:

. primarily 2-methyl-5ethylpyridine for the firstY four maf terials, 2,46-triphenylpyridine for the next, two, 2,4,65` collidine,4 (para-chlorophenyl) 2, -diphenylpyridine; i `and 4-anisyl-2,fdiphenylpyridine for each of :the others'reeY spcctively.

Generally a catalyst is used, and I prefer a-'tluorintf containing catalyst such as ammonium uoride, ammo nium bituoride, boron trifluorideV thesepreferably in-a' complex with ammonia or an amine; salts of uoroboric acid, salts of the fluorophosphoric acids, salts of triuorof acetic acidand-salts of fluosilicic acid@ However;- other. catalysts known in the art can be used such as ammonium chloride, ammonium acetate, alumina, sulfonic acids,etc.j

The-pyridine derivative made bythe above process of great commercial importance at the present Vtime--is MEP (Z-methyl-S-ethylpyridine) which can be madefby condensing paraldehyde with ammonia. MEP is useful as an intermediate inthe production of MVP (2-methyl-5r.v vinylpyridine) which has a host of uses in polymerization processes. For that reason, I will further explain my in -g vention by describing -it in an MEP synthesisprocess wherein paraldehyde is condensed with ammoniaV to -form This invention can best be described byreferring ,to the attached drawings `of which: l p s Figure l is a flow diagram of an MEP synthesisfprocg, ess showingschematically how myv invention is usedt in, such a process, Y. j w f au.

Figure 2 is a schematic vertical section ofthe absorber and controls `of my invention. The referencenumerals are .the same as used in Figure l for. the same elements;E Figure 3 -is a plot of ammonia concentration versus.' vapor pressure at various temperatures, and,

Figure 4 is a plotoftemperature against vapor presid ure for variousfaqueous ammonia concentration.

vReferring to Figure l, paraldehyde from surge Atzniklj isV pumped at about 2000 pounds per square Y,inchlglllgil` (p. s. i. g.) via pump 2 and conduit 3 to conduit whe it joins a stream of aqueous ammonia which.generaliy;` contains the condensation catalyst. The'pressur'e mustV Sucient to maintain Vthe reactantsas a liquid'phase t vammonia is flashed from the stream in Y 3 der reaction conditions and can vary from about 850 p. s. i. g. to over 2500 p. s. i. g. These reaction ingredients thenpassto preheater 5 where'the temperature is raised to 500 F. The temperatures generallyused'can range from 3507to 650 F. but are more commonly be-Y tween 450 and'550" F. The hot reaction ingredients pass Vvia conduit 6 to kreactor 7. The residence time inv the Vreactor is approximately minutes but contact'time can vary from 5 minutes'to several hours. The reactor 7 Vis divided into two YzouesAfandB. In zone A, both burners and coolers are used `to control the temperature 'since Vthe reaction is slightly exothermic but requires high temperature to proceed. In the zone B, only burners Vare used since the greater portionfof the reactants will react in zone A so that zone B Vis used forV additional resi'- dence time. The stream containing the reacted materials passes from reactor 7 via conduit 8, to pressure rewater and serves to maintain the absorber temperature at ducing valve 9 wherein the pressure is dropped Vto approx-pY imately160 p. s. Vi. g. This reduction in pressure cools the stream to Abetween 250-300 F. and at the same time vaporizes most of the ammonia vand part of the water.

' The stream isfurther cooled by means of cooler 10 and then passes to' ash vessel 11."Y A'large portion of the this vessel and is removed through conduit 12.

Y Y The water, MEP formed in the reactor, dissolved 'am-V Y monla .and condensation byproducts pass via conduits 13 and/14 to stripper 15 wherein most of theV remaining dis-V solvedammoniais driven off by heat through conduit 16z .The organic and aqueous pha-ses are passed via conduit 17 to vessel 18 where they are separated, the organic Yphasebeing removed via conduit19. The waterphase then Vpasses via conduit -20 to stripper 21 wherein the last traces of ammonia and dissolvedl pyridines'are removed viaY conduit 22 to accumulator 23. The water from stripperY 21 is sent--viavconduit 24 to recycle water tank 25. Water, pyridines and ammonia from accumulator 23 are returned tothe system via either conduits 26 andV 27 to the ammonia `Aflash to the stripper 15.

Ammonia fromV ash vessel 11Y and stripper 15 Vpasses via conduits 12Y and 16, respectively, to ammonia header conduit 29. Anhydrous ammonia from vessel 30 passes.

via conduits V31 and 32, ilow `control valve 33 and orifice 34 to said-header conduitY 29. The valvesin conduits 31 if desired, for example, when valve'33 is down for overhuL The amount of ammonia passing to conduit 29 from flash vessel 11 and stripper 15 varies with operating conditions so in order to control thertotalammonia passing to conduit 29, the ammonia from vessel 30 will` have to Vbe varied to compensate for fluctuations from the other two sources. Y This is done by Vmeans of valve 33 as will be later-shown.Y The ammonia from conduit 29V is introducedY into the bottom ofabsorber 35. At the same timeV Y water from-vessel'25 is introducedV into the top of absorber 35 'via conduit 36. The liquidY level is icontrolled in ab;

sorb'er 35 by means of level controller 37 whicli actuates valve 38 lin response Vto the levelfchange admitting more Y Y orlessV water. When asoluble catalyst is beingusedthe water from 'conduit' 36 canrpass tofoatalyst mixer 39 via conduit 40 where it'di'ssolves the'catalyst and returnstoY conduit'36 via conduit-41'..Y

VKThedesired*temperatureof theabsorber is about 115 i F, butit may be-any temperature Yfrom 90V F. tof 140'? F.

vessel 11 or via conduits Y26, 28V and 14V and 32 are provided so that'manual operation 'is possible the desired level. A temperature controller 50 is operably connected by a temperature sensing element in conduit V43. This controller is also operably connected to valve Y 51 and admits more or less coolant to cooler 44 in respouse to changes in temperature of liquid in conduit 43. `A. sealed bulb or cell'45 containing an aqueous solution of ammonia of a known concentration isinscrtelinV the liquid phase of the absorber 35. The aqueous solution in bulb 45 will be at the same ltemperature as the surrounding liquid. This bulb is connected to differential Y pressure controller 47 via conduit`46; VThe dilerential Y. f pressure controller is also connected tothe vapor V`zone ci Y absorber 35 via conduit 48.' This differential'pressure controller is in turn operably connected Vto ow recorder controller 49 which is in turn operably lconnected to orifice Y 34 and to control valve 33. TheV ow'recorder controllerV absorber. Since the known solutionin bulb 45 is blended Y to have av concentrationr inthe same rangerasdesiredrin the absorber,fonly a'small differential pressurewill exist Y between itA and theabsorber pressure, and this will'remairi true'in spite of temperature variations of the entire sys- K tem. If a differential pressure does occur, it willbe sensed Y.

andrthis control system will adjust the rate of fresh 'am-V rn'onianow in thedesired direction until'a differentialV pressure does not exist. Theaqueous solution is with-'f Y drawn from the absorber'viar conduitSS and passed to d pump 54 where therpres'sure is raised to approximately 2,000 p. s; i. g. and from whence it is introduced to con-'` duit 4 and issent tothe preheater 5 along with the paralgv dehyde from vessel 1.

' Theabsorber is equipped with a pressure controller 4 52 Whichrisv operably connected to valve'53 andV causesY this valve to open to vent in case the pressure exceeds Ythe Y safe Y'limit for `the vessel. Venting is normally ,required periodically to `purge inert or insolubrle'gases from the absorber.

numbers are the s ame as were used for the same elements Referring to Figure, Vthetotal vapor pressurepin Vpounds per vsquare inch absolute (p. s. i. a.), is plotted` L against theoweigh't percent ammonia inraqueous 'solutionV i f plus orminus 2 percent inV composition which wo'uld'l'ef soY long as the selected'temperatureis maintained reason-f f Y ably constant. "Ifthe temperature injthe absorber remains(V constant, Vthen'the pressure invapor phase C above the liquidrphase D willbedependent uponrth'e'concentraition of ammonia inthe liquid phase. However, since recycle. water containing noammonia is added continuously .tothey absorber, to obtain near equilibrium relations of the vapor YVafudjrliquid phases,V the liquid Dis recirculated at a mode- Y atvvarious temperatures. The slope ofthe. curve betweenVA 30 and; 40 weight percentammoniain waterat 115 'is/ 2.5 p.js; 4i.'clxange in vapor pressure. for'eachfpercent ehangeinpcompo'sition. Y `The system can tolerate afchange equivalentto plusworminus'p. Vs. i; change in pressureY at1`15vjF. The V,differential pressure controller .4777,1of` l Figures 1iand`2 should detect a changeof plus or minus y1 p.Y s. i. or less and Atherefore thesensitivityrof the appara#Y tusisiveUgwitbin the tolerabkY COWPOSQ 'limits' Referees @Figure 4s therapr pressure; in pouds Vpersquare;'inch absolute (pys. i.p-a.), is plotted against temperaturegfor various Vconcentration Yof aqueous solu-V Y tions. .Iviitiisudesired to hold'the ammonia concentration Y @35./weight percentandlllS" F. inthe liquidV phase in the absorbergfthere will be exerted 39 p. s. i. a. vapor pres' Y f sure', l Nou/, the known solution in sealed bulb 45 (Fig-iv` ures' l audp2)is "30A weight,V percent, 'thepressurein the Y bulb is appoximately'ZS p. s. i, aJor a .difference registered 'l on thediterential pressurecontroller ofA -fl-llp, Us. i. In g '"fpercenf, thefdierential Vpressure controllerl bes'etV Yarder t0 ihojlda liQDidrhaS;concentration of '35 .weightis an enlarged sectionof that part of Figure '1: showing 4the absorberS andthe control apparatus. VThe A vfor +11 p. s. i. differential. If the operating temperature level of the absorber changes to 130 F., the solution in the sealed bulb 45 will then exert 37 p. s. i. a. vapor pressure and the desired +11 p. s. i. differential pressure will control-the absorber so as to produce an aqua ammonia of 48 p. s. i. a..vapor pressure at 130 F. corresponding to about 34 weight percent ammonia. This error arises from the slope of the vapor pressure versus composition curve (Figure 3) at 130 F., whose slope is about 3 p. s. i. per l percent ammonia. Similarly at 90 F. since the slope is about 1.5 p. s. i. per 1 percent, the aqua ammonia solution producedat +11 p. s. i. differential pressure will be 37.5 weight percent. The examples cited are extreme, since in practice the solution in the sealed bulb will be selected so that the differential pressure controller will need to be set to control at only a few pounds diierential, not over l or preferably a zero differential. Also the temperature will be controlled so as not to vary more than plus or minus 5 degrees and preferably plus or minus 2 degrees. Since the pressure in the bulb is the base pressure, pressures above this are considered plus differentials.

l have described my invention in terms of one of its preferred embodiments. Those skilled in the art will see many modiiications which can be made without departing from the scope of this invention. For example, it is within the skill of the art to supply the necessary valves, pressure regulators, pumps, relief valves and the like.

I claim:

l. The process for preparing an aqueous ammonia solution of concentration within a predetermined weight percent range, said process comprising continuously introducing ammonia into the lower section of an absorption zone, continuously introducing a liquid aqueous medium into the upper section of said absorption zone, maintaining a liquid level in said absorption zone above the level of introducing said ammonia and below the level of introducing said aqueous medium so as to divide said absorption zone into a liquid phase zone and a vapor phase zone, detecting the differential pressure between the vapor pressure of an aqueous solution of ammonia of known concentration submerged in said liquid phase and the vapor pressure of said vapor phase, regulating the flow of said ammonia to said absorption zone in response to changes in said dilerential pressure, contacting said introduced ammonia with said aqueous medium in said absorption zone, and continuously withdrawing resulting aqueous ammonia solution from the bottom of said absorption zone.

2. The process of claim 1 wherein a portion of the said withdrawn aqueous amomnia solution is added to the said aqueous medium being introduced into said absorption zone and wherein the resulting mixture is sprayed downward through the said vapor phase.

3. The process for preparing an aqueous ammonia solution of a concentration within a predetermined weight percent range, said process comprising continuously introducing a stream of ammonia into the lower section of an absorption zone, the said lower section containing therein a capsule containing an aqueous solution of ammonia of known concentration; the said ammonia stream being comprised of plurality of ammonia streams of which at least one is independently variable, continuously introducing a liquid aqueous medium into the upper section of said absorption zone, gravitating said liquid downward to form a liquid pool in said absorption zone, detecting the level of said pool, controlling the rate of introducing said aqueous medium to said absorption zone in response to said liquid level variations so as to maintain said liquid level above the level of introducing said ammonia and above the said capsule containing aqueous amonia and below the level of introducing said aqueous medium so as to form a liquid phase and a vapor phase in said absorption zone, allowing the aqueous ammonia in said capsule to come in temperature equilibrium with said liquid phase, detecting the, differential` pressure, `,between the vapor pressure o'f the-said aqueous ammonia of known concentration and the vapor pressure of the said vapor phase in said absorption zone, regulating` the `ow of ammonia ,of a`second of the said plurality of ammonia streams in response to variations in saiddiferential pressure from a predetermined pressure dilerential, contacting said introducedammonia stream with said aqueous medium insaidabsorption zone thereby forming an aqueous solution of ammonia in said absorption zone, continuously withdrawing aqueous ammonia from said absorption zone, vand taking a portion of said withdrawn aqueous ammonia and adding it to the said aqueous medium being introduced to the absorption zone.

4. The process of claim 3 wherein the portion of aqueous ammonia being added to the aqueous medium is iirst cooled to a predetermined temperature and wherein the predetermined differential pressure is no greater than ten pounds per square inch.

5. An apparatus for producing aqueous ammonia of a predetermined concentration, said apparatus comprising in combination an absorption vessel, means for introducing ammonia into a lower section of said Vabsorption vessel, means for introducing liquid into an upper section of said absorption vessel, means for detecting liquid level in said absorption vessel,- means for controlling low through said means for introducing liquid in said upper section, said controlling means being operably connected to and responsive to said means for detecting said liquid level, a cell containing an aqueous ammonia solution of known concentration disposed in said absorption vessel below said liquid level, a dilerential pressure controller operably connected with said cell and said absorption vessel above said liquid level so as to be responsive to the dierence in vapor pressure between said cell and said vessel, a ow regulator operably connected in said means for introducing ammonia into said absorption vessel, said ow regulator being operably connected to and responsive to said differential pressure controller, and means for removing liquid from bottom of said absorption vessel.

6. An apparatus for producing aqueous ammonia of a predetermined concentration, said apparatus comprising in combination an absorption vessel, means for introducing ammonia into a lower section of said absorption vessel, means for introducing liquid into an upper section of said absorption vessel, means for detecting liquid level in said absorption vessel, means for controlling ow through said means for introducing liquid in said upper section, said controlling means being operably connected to and responsive to said means for detecting said liquid level, a cell containing an aqueous ammonia solution of known concentration disposed in said absorption vessel below said liquid level, a diierential pressure controller operably connected with said cell and said absorption vessel above said liquid level so as to be responsive to the difference in vapor pressure between said cell and said vessel, a ow regulator operably connected in said means for introducing ammonia into said absorption vessel, said ow regulator being operably connected to and responsive to said diierential pressure controller, and means for removing liquid from bottom of said absorption vessel, means for circulating a portion of said withdrawn liquid to said means for introducing liquid into said absorption vessel, means for cooling operably connected in said circulating means, a temperature coutroller, a temperature sensing device in said circulating means and operably connected to said temperature controller, and said cooling means being operably connected to said temperature controller responsive to temperature changes.

7. The apparatus of claim 6 wherein the means for introducing liquid into said upper section of said absorp-` tion vessel is a spraying device.

r7 8.'The"pparatus ofY c1aim 7 wherein 'the rneansfor introducing .ammonia into sid lower sectionof said absorption vessel is comprised of yaplurality of conduits connecting with a singleheader wherein the singleheader enters said bsorption vessel, and wherein said ow regulator is connected iin one of said plurality of conduits.

References Cited in the le of this patent UNITED STATES PATENTS Y 48 Schmidt Aug. 4,1936 ,Guthniann Aug. 13,1940 Binnington Apr.V 17, 1945 Marks'on June 29, 1948 Bourdon Apr.V 3, 1951 .Hoog July 29,' 1952 Mahan Oct. 21,' 1952 Harrison Apr. 20, 1954' FOREIGN PATENTS Y Germany Apr. 30, 19,13 Great BritainY Y.. `Tuly 17, 191.9 

1. THE PROCESS FOR PREPARING AN AQUEOUS AMMONIA SOLUTION OF CONCENTRATION WITHIN A PREDETERMINED WEIGHT PERCENT RANGE, SAID PROCESS COMPRISING CONTINUOUSLY INTORDUCING AMMONIA INTO THE LOWER SECTION OF AN ABSORPTION ZONE, CONTINUOUSLY INTRODUCING A LIQUID AQUEOUS MEDIUM INTO THE UPPER SECTION OF SAID ABSORPTION ZONE, MAINTAINING A LIQUID LEVEL IN SAID ABSORPTION ZONE ABOVE THE LEVEL OF INTRODUCING SAID AMMONIA AND BELOW THE LEVEL OF INTRODUCING SAID AQUEOUS MEDIUM AS AS TO DIVIDE SAID ABSORPTION ZONE INTO A LIQUID PHASE ZONE AND A VAPOR PHASE ZONE, DETECTING THE DIFFERENTIAL PRESSURE BETWEEN THE VAPOR PRESSURE OF AN AQUEOUS SOLUTION OF AMMONIA OF KNOWN CONCENTRATION SUBMERGED IN SAID LIQUID PHASE AND THE VAPOR PRESSURE OF SAID VAPOR PHASE, REGULATING THE FLOW OF SAID AMMONIA TO SAID ABSORPTION ZONE IN RESPONSE TO CHANGES IN SAID DIFFERENTIAL PRESSURE, CONTACTING SAID INTRODUCED AMMONIA WITH SAID AQUEOUS MEDIUM IN SAID ABSORPTION ZONE, AND CONTINUOUSLY WITHDRAWING RESULTING AQUEOUS AMMONIA SOLUTION FLOW FROM THE BOTTOM OF SAID ABSORPTION ZONE. 